/*-------------------------------------------------------------------------
 *
 * logtape.h
 *    Management of "logical tapes" within temporary files.
 *
 * See logtape.c for explanations.
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/logtape.h
 *
 * -------------------------------------------------------------------------
 */

#ifndef LOGTAPE_H
#define LOGTAPE_H

#include "storage/sharedfileset.h"

/* LogicalTapeSet is an opaque type whose details are not known outside logtape.c. */

typedef struct LogicalTapeSet LogicalTapeSet;
typedef struct LogicalTape LogicalTape;

/*
 * The approach tuplesort.c takes to parallel external sorts is that workers,
 * whose state is almost the same as independent serial sorts, are made to
 * produce a final materialized tape of sorted output in all cases.  This is
 * frozen, just like any case requiring a final materialized tape.  However,
 * there is one difference, which is that freezing will also export an
 * underlying shared fileset BufFile for sharing.  Freezing produces TapeShare
 * metadata for the worker when this happens, which is passed along through
 * shared memory to leader.
 *
 * The leader process can then pass an array of TapeShare metadata (one per
 * worker participant) to LogicalTapeSetCreate(), alongside a handle to a
 * shared fileset, which is sufficient to construct a new logical tapeset that
 * consists of each of the tapes materialized by workers.
 *
 * Note that while logtape.c does create an empty leader tape at the end of the
 * tapeset in the leader case, it can never be written to due to a restriction
 * in the shared buffile infrastructure.
 */
typedef struct TapeShare {
    /*
     * firstblocknumber is first block that should be read from materialized
     * tape.
     *
     * buffilesize is the size of associated BufFile following freezing.
     */
    long firstblocknumber;
    off_t buffilesize;
} TapeShare;

/*
 * prototypes for functions in logtape.c
 */

extern LogicalTapeSet *LogicalTapeSetCreate(int ntapes, TapeShare *shared, SharedFileSet *fileset, int worker);
extern LogicalTapeSet *LogicalTapeSetCreate(SharedFileSet *fileset, int worker);
extern void LogicalTapeClose(LogicalTape *lt);
extern void LogicalTapeSetClose(LogicalTapeSet *lts);
extern void LogicalTapeSetCloseOnly(LogicalTapeSet *lts);
extern void LogicalTapeSetForgetFreeSpace(LogicalTapeSet *lts);
extern size_t LogicalTapeRead(LogicalTapeSet *lts, int tapenum, void *ptr, size_t size);
extern size_t LogicalTapeRead(LogicalTapeSet *lts, LogicalTape *lt, void *ptr, size_t size);
extern void LogicalTapeWrite(LogicalTapeSet *lts, int tapenum, void *ptr, size_t size);
extern void LogicalTapeWrite(LogicalTapeSet *lts, LogicalTape *lt, void *ptr, size_t size);
extern void LogicalTapeRewindForRead(LogicalTapeSet *lts, int tapenum, size_t buffer_size);
extern void LogicalTapeRewindForRead(LogicalTapeSet *lts, LogicalTape *lt, size_t buffer_size);
extern void LogicalTapeRewindForWrite(LogicalTapeSet *lts, int tapenum);
extern void LogicalTapeFreeze(LogicalTapeSet *lts, int tapenum, TapeShare *share = NULL);
extern void LogicalTapeFreeze(LogicalTapeSet *lts, LogicalTape *lt, TapeShare *share = NULL);
extern void LogicalTapeSetExtend(LogicalTapeSet *lts, int nAdditional);
extern size_t LogicalTapeBackspace(LogicalTapeSet *lts, int tapenum, size_t size);
extern size_t LogicalTapeBackspace(LogicalTapeSet *lts, LogicalTape *lt, size_t size);
extern void LogicalTapeSeek(LogicalTapeSet *lts, int tapenum, long blocknum, int offset);
extern void LogicalTapeSeek(LogicalTapeSet *lts, LogicalTape *lt, int64 blocknum, int offset);
extern void LogicalTapeTell(LogicalTapeSet *lts, int tapenum, long *blocknum, int *offset);
extern void LogicalTapeTell(LogicalTapeSet *lts, LogicalTape *lt, long *blocknum, int *offset);
extern long LogicalTapeSetBlocks(LogicalTapeSet *lts);
extern LogicalTape *LogicalTapeCreate(LogicalTapeSet *lts);
extern LogicalTape *LogicalTapeImport(LogicalTapeSet *lts, int worker, TapeShare *shared);

#endif /* LOGTAPE_H */